Auto merge of #13412 - GnomedDev:regex-comp-in-loop, r=y21

Implement lint for regex::Regex compilation inside a loop

Closes #598.

Seems like a pretty simple one, I'm not sure if I sorted out all the lint plumbing correctly because I was adding it to the existing regex pass, but seems to work. The name is a bit jank and I'm super open to suggestions for changing it.

changelog: [`regex_creation_in_loops`]: Added lint for Regex compilation inside loops.

tests/ui/regex.rs

@@ -5,7 +5,7 @@
     clippy::needless_borrow,
     clippy::needless_borrows_for_generic_args
 )]
-#![warn(clippy::invalid_regex, clippy::trivial_regex)]
+#![warn(clippy::invalid_regex, clippy::trivial_regex, clippy::regex_creation_in_loops)]
 
 extern crate regex;
 
@@ -118,7 +118,35 @@ fn trivial_regex() {
     let _ = BRegex::new(r"\b{start}word\b{end}");
 }
 
+fn regex_creation_in_loops() {
+    loop {
+        static STATIC_REGEX: std::sync::LazyLock<Regex> = std::sync::LazyLock::new(|| Regex::new("a.b").unwrap());
+
+        let regex = Regex::new("a.b");
+        //~^ ERROR: compiling a regex in a loop
+        let regex = BRegex::new("a.b");
+        //~^ ERROR: compiling a regex in a loop
+        #[allow(clippy::regex_creation_in_loops)]
+        let allowed_regex = Regex::new("a.b");
+
+        if true {
+            let regex = Regex::new("a.b");
+            //~^ ERROR: compiling a regex in a loop
+        }
+
+        for _ in 0..10 {
+            let nested_regex = Regex::new("a.b");
+            //~^ ERROR: compiling a regex in a loop
+        }
+    }
+
+    for i in 0..10 {
+        let dependant_regex = Regex::new(&format!("{i}"));
+    }
+}
+
 fn main() {
     syntax_error();
     trivial_regex();
+    regex_creation_in_loops();
 }

tests/ui/regex.stderr

@@ -195,5 +195,55 @@ LL |     let binary_trivial_empty = BRegex::new("^$");
    |
    = help: consider using `str::is_empty`
 
-error: aborting due to 24 previous errors
+error: compiling a regex in a loop
+  --> tests/ui/regex.rs:125:21
+   |
+LL |         let regex = Regex::new("a.b");
+   |                     ^^^^^^^^^^
+   |
+help: move the regex construction outside this loop
+  --> tests/ui/regex.rs:122:5
+   |
+LL |     loop {
+   |     ^^^^
+   = note: `-D clippy::regex-creation-in-loops` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::regex_creation_in_loops)]`
+
+error: compiling a regex in a loop
+  --> tests/ui/regex.rs:127:21
+   |
+LL |         let regex = BRegex::new("a.b");
+   |                     ^^^^^^^^^^^
+   |
+help: move the regex construction outside this loop
+  --> tests/ui/regex.rs:122:5
+   |
+LL |     loop {
+   |     ^^^^
+
+error: compiling a regex in a loop
+  --> tests/ui/regex.rs:133:25
+   |
+LL |             let regex = Regex::new("a.b");
+   |                         ^^^^^^^^^^
+   |
+help: move the regex construction outside this loop
+  --> tests/ui/regex.rs:122:5
+   |
+LL |     loop {
+   |     ^^^^
+
+error: compiling a regex in a loop
+  --> tests/ui/regex.rs:138:32
+   |
+LL |             let nested_regex = Regex::new("a.b");
+   |                                ^^^^^^^^^^
+   |
+help: move the regex construction outside this loop
+  --> tests/ui/regex.rs:137:9
+   |
+LL |         for _ in 0..10 {
+   |         ^^^^^^^^^^^^^^
+
+error: aborting due to 28 previous errors